


Slime Cube Knows Best

by Spiderlily_Writes



Category: Fire Emblem: Fuukasetsugetsu | Fire Emblem: Three Houses
Genre: Exhibitionism, F/F, Kinda?, Monster sex, Multiple Penetration, Slime
Language: English
Status: Completed
Published: 2021-01-18
Updated: 2021-01-18
Packaged: 2021-03-16 01:41:22
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,252
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/28823127
Author URL: https://archiveofourown.org/users/Spiderlily_Writes/pseuds/Spiderlily_Writes
Summary: Constance has created a new product, sure to be a hit, certain to fill her coffers enough to restore House Nuvelle to its former glory. Hapi is...a little skeptical, but supportive.
Relationships: Hapi/Constance von Nuvelle
Comments: 18
Kudos: 62





	Slime Cube Knows Best

**Author's Note:**

  * For [whaleandjanuary](https://archiveofourown.org/users/whaleandjanuary/gifts).



> Hi all! This was so much fun to write, I hope you like it. Also, coincidentally, it's the weekend after Hapi's birthday! Happy birthday, I got you "being fucked by a slime monster".

“Coco, are you like, _sure_ this thing is safe?” Hapi asks, skeptical. She reaches out with one hand, extends a finger, and nearly pokes it, but draws back at the last second as though afraid it will bite her. “I’m just saying, not all of your projects turn out like you want ‘em to.”

“Oh, Hapi, my dear,” she says, in a way that Hapi thinks is supposed to sound reassuring, but really just seems more like bravado. “I promise you this is perhaps the _safest_ thing I have ever created. It’s a _relaxation_ aid; how could that possibly go wrong?”

Hapi looks to the container full of…something. “Well, I mean…there’s a lot of it,” she points out. “And, I dunno, can you drown in something like this?”

The container is a box, made out of metal, that stands about five feet tall. The square-footage is about twice that, and it’s big enough that Hapi could lie down, spread-eagle, in the middle, and not touch any of the sides. Really, even someone Balthus’s size could.

The box itself isn’t what Hapi is worried about, though; she’s more concerned by the _contents_ of the thing. It’s filled, nearly to the brim, with some kind of light-blue watery compound that seems to have about the same consistency as a flan.

What’s _really_ worrying, though, is that it seems to be _moving_. There’s no wind down in Abyss, especially not in the small side-room that Constance has commandeered for her project, so how it’s managing to move is something of a mystery. It just sort of…jiggles, every once in a while.

“Of course not, silly,” Constance replies, tapping the side of the container affectionately. “It knows better than to pull someone under. That would sort of defeat the purpose of a relaxation aid, don’t you think?”

Hapi blinks.

“It…knows?” She takes a step back and looks at the tank again. “What do you mean ‘it knows’? I thought this was just like, I dunno, a warm, thick bath? What does it _know_?”

Constance blushes slightly. “Well, you see, it’s…I mean…the enchantment may have bestowed upon it _some_ small degree of sentience. Perhaps. I have yet to find out. But rest assured, even if it _does_ know things, it has only the best of intentions. And it’ll push you out if you ask politely.”

There’s a moment of silence between the two. Hapi narrows her eyes suspiciously. Constance’s blush intensifies, and she coughs a little.

“Besides, Hapi, you were telling me just the other day how stressed you were. I can promise with one-hundred percent certainty that this will help. In fact, I would be willing to gamble the good name of House Nuvelle on it!” Constance says, and she _does_ sound pretty confident. Not to mention, Hapi _has_ been feeling pretty high-strung lately.

“Alright, fuck it, sure. I’ll get in the jelly cube.”

Her girlfriend beams, and that’s all the encouragement she needs.

“Wonderful! I need only remove the sides, and then it should be a simple matter to just step in!” Constance moves to the corners of the container, where she carefully flicks a few latches open and pulls the sides of the box away, laying them gently on the floor. She flinches slightly as she lets down the first side, but, sure enough, the cube stays put. Once the thing is fully exposed, Constance takes a step back, pulling out a journal and pencil and watching Hapi expectantly.

Hapi stares at it, unsure how to proceed. “So…do I just…step in?” she asks, extending a hand toward the cube. It’s warm to the touch, like a bath that’s at the perfect temperature, and the jelly itself actually feels pretty nice. It’s a little firmer than she expected, but that’s fine.

“Yes, you should be able to just—” Constance begins, but she’s cut off when Hapi cries out in surprise. The moment her hand penetrates the cube to the wrist, she’s abruptly yanked off her feet and dragged inside.

Reflexively, Hapi closes her eyes, but she needn’t have bothered, because her head never quite goes below the surface. When she opens them again, she finds that she’s dead-center, with only her head poking out from the top of the cube.

What’s more, she’s not _quite_ on her feet, as when she was wrenched into the mass, she came slightly off the ground. But it doesn’t matter, because she finds herself completely unable to move her legs—or her arms, actually. It’s an incredibly strange feeling, almost like being held in place by very firm hands, except that pressure is being exerted on every inch of her body equally.

Trying not to panic, she looks to Constance, who has dropped her notebook in surprise.

“Hey, Coco? Is it, uh, supposed to do that?” she asks, nervous. Constance clears her throat, and picks her notebook up off the floor.

“Well, no, not exactly,” she admits, sheepishly. “It seems to be _slightly_ more aggressive than I had accounted for. Is it hurting you?”

Hapi thinks about that for a second.

“Nope,” she says, surprised. “I mean, it scared me a little, but it doesn’t hurt. I can’t move, though.”

Constance nods, jotting something down in her notes, then looking back up. “Of course, that makes sense. It seems to have very strong ideas about how you ought to relax. I would suggest trying to remain calm, so that we might see what it does!”

She sounds enthusiastic and excited again, which is good; that alone puts Hapi more at ease. So she closes her eyes, and focuses on what she can feel around her. “Still don’t now how I feel about the slime cube having ‘ideas’ about anything,” she mumbles.

The first thing she notices is more pressure. It’s not unpleasant—far from it, actually, almost as though the cube is giving her a massage. It applies and releases pressure at different points on her body in patterns that make her feel less tense almost immediately, and she hums in pleasure.

“How does it feel?” Constance asks, just loud enough to be heard. Seems like she doesn’t want to interrupt Hapi’s relaxing-time more than she has to.

“Real nice. It’s like…a backrub? Almost? It’s hard to explain, you should get in too,” she replies. Hapi is becoming less bothered by the restrictive nature of the cube each second that this massage continues, really. Cube knows best.

Constance laughs. “Hapi, I can’t! Someone has to record the results of the experiment, for posterity! And you seem as though you are perhaps just a little bit indisposed, at the moment, so _you_ certainly won’t be the one doing that.”

“Whatever floats your goats,” Hapi murmurs, and she feels her position adjusting inside the jelly. It moves her arms out to her sides, slightly, almost as though she’s sitting in an armchair. “I think you struck gold with this one, Coco, this is great. Like a hot bath that gives you a massage.”

All of a sudden, she feels a tingling sensation on her skin. It’s just for a moment, but when it abates, she can feel the jelly more…completely? Whatever. Doesn’t matter. At least, it doesn’t until she hears Constance gasp.

“Oh, good heavens! Hapi, I…ah…” she exclaims, and that surprise is enough to make Hapi open her eyes, interrupting her near-doze. She sees Constance standing there, one hand over her mouth, face more flushed than Hapi has ever seen her.

“What is it? Did something…” she begins, but she trails off as she looks down and sees that her clothes have simply disappeared. She was definitely wearing them before she climbed into the cube; Constance hadn’t said anything about needing to be naked for _this_ particular experiment. Nonetheless, though, she’s not wearing a single scrap at the moment, and the way she could suddenly feel the jelly’s ministrations more acutely makes a little more sense. “Did it _dissolve_ my clothes?” she asks, thoroughly confused. “Should it be able to do that?”

“It…certainly seems as though it has dissolved your clothes, yes,” Constance confirms, blinking. “You are still unhurt, correct?”

“Yeah. Whatever it did, seems like it only affects cloth? I’m glad I didn’t dress nice today or anything.”

Constance writes another note. “Very good. In the future, we shall simply ensure that anyone who enters the cube does so without clothing.”

Hapi frowns. “Yeah, I guess, but why would it—” she begins, but her question is answered mere moments later. The cube, apparently, hasn’t finished moving her yet. She feels it lifting up on her legs, spreading them slightly apart, exposing her to Constance through the almost completely transparent jelly.

She feels her face heat up, and Constance seems to be more intensely focused on that _particular_ area of the cube than she was, before. “Hey, come on, it’s not like you haven’t seen me naked before,” she complains.

“I have seen the moon before as well, but I appreciate it no less on repeated viewings,” she insists, holding up her pencil-hand to half-cover a sly smile. Hapi groans, but her eyes go wide and she gasps as she feels the mass of the jelly shift once more.

Her arms and legs are still held firmly in place by that warm, gentle-but-unyielding pressure, but there’s a new, different sort of sensation as well. It’s more direct, less subtle, and it’s acute, rather than enveloping.

It starts like trailing fingers at her collarbone, and she hums softly, trusting the cube to do its thing. Constance is watching, clearly fascinated, and if Hapi is being _totally_ honest, she might have a little tiny bit of a thing for exhibitionism that’s being tickled in just the right way.

The interesting thing about the jelly, she supposes, is that unlike a person, it is not limited in how many parts of her it can touch at a time. As she feels the caressing sensation travel down her torso and between her breasts, she notices several more pinpricks of pressure in various other places; her thighs, her back, her feet, her ass, each application of force feeling _slightly_ different.

On her thighs, it’s a harder push, almost like a _raking_ sensation, like when Constance drags her nails across the skin there. Somehow, the jelly intuits that she enjoys that, and continues to do it, moving slowly, but purposefully. On her feet, it’s a more simple, gentle caress on the tops and soles. It doesn’t tickle, it feels more like soft kisses, in fact.

Her back feels similar to before, as though she’s receiving a massage, but every once in a while, she can feel that same raking-of-nails that continues to tease at her inner thighs.

And…her backside. Well. _That’s_ the most interesting of any of them. She can feel the jelly, almost like a pair of hands, cupping her backside and squeezing slightly. Then, all of a sudden, she feels what she would _swear_ is a gentle swat there, enough to make her yelp. When Constance looks at her, quizzically, she tries to explain.

“I…it uh…just spanked me, I think?” she says, fully understanding how strange that probably sounds. Constance nods, brows furrowed in focus, and jots down another note. Hapi could _swear_ that Constance is fidgeting slightly, shifting from foot to foot in a way that produces a bit of friction on her legs. “Hey, Coco. Are you getting off on this?” Hapi asks, and by the way that her girlfriend gapes at her and tries to sputter an excuse, she’d say she hit the mark _perfectly_. She grins at Constance, and the grin rapidly turns into a soft, open-mouthed gasp as the sensations shift again.

“Don’t w-worry,” Hapi assures her. “Me too.”

The jelly has apparently decided she can take a little more, because she feels a pressure on her left breast, almost as though she’s being groped _just_ firmly enough to be enjoyable. Then her right. Then both at once. And then, in a move that makes her moan aloud, she feels a hard, insistent _sucking_ sensation on both of her nipples, followed by a brief _pinch_. She would squirm, if she could, but she has to settle for groaning and wiggling her fingers.

“Does…does it still feel nice?” Constance asks, and there’s naked desire in her voice now. Hapi nods, furiously.

“Uh, yeah, it really fucking does,” she says, gasping as the jelly repeats its systematic assault on her chest. “It’s like…having a whole bunch of people all touching me at once, and they all know _exactly_ what I like. It’s amazing, Coco.”

Constance closes her notebook and tosses it gently aside, onto an old rickety table. One of her hands slowly finds its way to the front of her skirt, where she trails it up her thigh. “H-Hapi, would you be offended if I—”

“Nope.”

“Very well, I…must confess, I did not expect this experience to be such a viscerally arousing one for the observer,” she says, rubbing at herself slightly, through the fabric.

Moments later, Hapi cries out, sharp and desperate, as a new sensation joins the rest: a firm, insistent, powerful stroking of her clit. She clenches her hands into fists, whimpering softly. “C-Coco, I think it’s actually going to fuck me,” she whines.

Sure enough, yet _another_ bit of pressure joins the last. She feels _something_ , pressing at her cunt, insistently, and of course since it’s not exactly solid, it penetrates her easily. “Holy shit,” she breathes, looking up at the ceiling, trying to collect herself as the pressure, just the right ‘size’, slowly begins to fuck her. The rhythm, of course, is perfect, and it’s only intensified by the attention being paid to her clit and basically every erogenous zone on her body from her neck down.

And _just_ when she thinks it might be done, right when she thinks there might be some relief coming, she is proven very, very wrong. She feels something pressing against her from behind, a pressure not unlike the one quite literally fucking the stress out of her. Easy as breathing, it slips inside her there, too. Hapi gasps, squeezing her fingers tight, toes curling at the unfamiliar but not unpleasant sensation.

“Hapi? A-Are you well?” Constance asks, upon hearing the noises her partner is making. Reasonable. Hapi doesn’t think she’s ever been attended to quite so _thoroughly_ before. Constance is great, of course, and she’s had other partners before, but no matter how good a person is, they’re still a person. No human would be capable of the omnidirectional sensory assault that this fucking cube is able to provide.

She groans as the penetration intensifies, the ‘girth’ of the masses within her beginning to swell slightly as she relaxes her muscles even more. “Yeah, Coco, I’m doing absolutely _great_. In fact…Fuck, the only thing that could make it better would be…”

And the thing can apparently sense her _thoughts_ , too, because with a very wet _splorch_ , it extends an honest-to-Goddess tentacle from its side, which it wraps around a very surprised Constance. Coco yelps, and looks for a moment like she might push herself away. It wouldn’t be _hard_ to do so, after all; while the tentacle is fairly solid, it would almost certainly break if she resisted even slightly.

But she doesn’t.

Instead, Constance takes a deep breath and closes her eyes as the jelly-thing yanks her close, pulling her into its mass in such a way that, like Hapi, only her head is poking out.

 _Unlike_ Hapi, though, the jelly creature—because at this point, it’s _definitely_ got to be a creature, rather than an object—melts away Constance’s clothing immediately and wastes no time in re-positioning her.

Constance gasps as she finds herself just as nude as Hapi, and again as her body gets manipulated into position so that she’s ‘laying’ atop her. Their torsos aren’t actually touching, of course, because that would displace the goo that’s been teasing Hapi in just the right way, and would prevent it from doing the same to Constance. There are mere inches between the two of them, though, and so Hapi can tell from the rapidfire expressions that cross Coco’s face that the jelly-cube has begun working on her just as intensely.

“O-Oh, Hapi, this feels…it feels—” Constance begins, then interrupts herself with a sharp, surprised cry. “Oh! Hapi! It also…it…”

“Yeah, goes for your butt, too. You get used to it,” she hums. The only thing Hapi had done was _consider_ how nice it would be for Constance to be here, because she’d really like to kiss her at the moment, and the thing had reacted immediately. “Doesn’t it feel good, though? I’m serious, Coco, you r-really aced this one.”

It’s getting difficult to speak properly as the jelly cube works her closer and closer to what’s probably gonna be the best orgasm of her entire life. Her eyes go wide as that unrelenting, unabating pleasure begins to build deep in her lower belly and swell.

“Coco, I’m…I’m gonna…” she manages to squeak out, and _Goddess_ , how she’d like to—

The creature reacts to her again, nudging Constance just a _little_ bit closer. Her girlfriend catches on immediately, because damned if _she_ can’t read Hapi’s thoughts, too. Coco’s lips press against her own in a deep, heady, open-mouthed kiss that stifles Hapi’s cries as she’s sent over the edge.

It feels wonderful, even as all her muscles tense and release and she whines into her kiss with Constance. It seems like it might go on forever, too, the waves of pleasure continuing to roll through her body with the same unabating insistence that the jelly cube had originally assailed her. She’s pretty sure Constance comes, as well, because her cries are returned with interest within a few seconds, and she feels the mass of the jelly cube shift slightly. Of the two of them, Constance tends to have the more physically dramatic orgasms, and it seems like it’s enough to actually fight the thing’s hold a little.

It works her through it, tensing and relaxing around her body in time with the pulses of her climax, and that only draws it out even longer. When the sensation _finally_ begins to taper off, she goes completely limp, utterly spent, and unable to think about _anything_ other than the warmth around her, and Constance’s lips pulling away from her own with a particular reluctance.

Constance—who seems equally limp and pliable—gets turned around, so her back is to Hapi’s front, and the jelly creature lays the blonde atop her. It holds them both firm and steady, though, and Hapi closes her eyes once more, just floating. It’s similar to being in a bath, now, except she can’t touch the bottom, and there’s plenty of room for them both to spread out.

“I don’t think…” Hapi mumbles, surprised by how low and mellow her own voice is. “…that I ever want to get out of here. Can I just live here now? Make my home in the fuck-slime?”

Coco titters softly, sounding equally mellow, which is new for her. “Hapi, don’t be crude. But…it seems like my experiment was a success.”

They drift together for a moment, simply enjoying each other’s company. Hapi eventually breaks the silence as she has, like, the best idea _ever_.

“Hey, Coco?”

“Mm?”

“How are we gonna get Yuri down here?”

**Author's Note:**

> Thank you very much for reading! If only we could _all_ get fucked by a slime monster, right? If you would like to follow me on twitter, find me [@spiderlilywrite](https://twitter.com/spiderlilywrite).
> 
> P.S.: You have my explicit permission to use the fuck slime in your own fics. My only request is that you tweet at me and tell me so I can read it.


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